1. Field of the Invention
The present invention relates to a method of detecting the width of a laminar flow. More particularly, the invention relates to a method of detecting the widths of a plurality of laminar flows formed in a channel, a method of controlling the width of a laminar flow, a system for controlling a laminar flow, and a flow cytometer.
2. Description of the Related Art
In recent years, a technology for causing bio-particulates such as cells and microorganisms, particulates such as microbeads, or the like to flow in a two-dimensional or three-dimensional channel formed on a plastic, glass or other substrate, detecting the particulates or the like by a physical means, an optical means or the like, and analyzing and separating the particulates or the like, has been advanced.
The above-mentioned technology has already become one of important basic technologies in diagnosis of diseases, screening of compounds such as drugs, forensic medicine, comprehensive analysis of genetic information, functional analysis of bio-substances, proteome analysis, analysis of in-vivo reactions, food industries, agricultural field, engineering fields, criminal identification field, etc. As one representative example of the method for analyzing or separating particulates or the like by use of a channel as above-mentioned, the analytical method called flow cytometry will be described below.
The flow cytometry is an analytical method in which particulates or the like to be analyzed are caused to flow in a fluid so as to form a row of the particulates, the particulates arrayed in a row are irradiated with a laser beam or the like, and the fluorescence or scattered light generated from each of the particulates is detected so as to analyze the particulates, and, further, the particulates are fractionally collected according to the analytical results.
Now, the flow cytometry will be described in detail below referring to FIG. 18. FIG. 18 is a schematic illustration of the concept of flow cytometry according to the related art. The process of flow cytometry can be largely divided into (i) water flow system, (ii) optical system, (iii) electric system, and (iv) fractional collection system.
(i) Water Flow System
In the water flow system (i), the particulates to be analyzed are arrayed in a row in a flow cell (channel) (see (i) in FIG. 18). More specifically, sheath flows F200 are made to flow at a fixed velocity in the flow cell, and, under this condition, a sample flow F100 containing the particulates is made slowly to flow into a central part of the flow cell. In this instance, by the principle of laminar flow in the channel, the respective flows do not mix with each other, and layer-formed flows (laminar flows) are formed. Then, the inflow quantities of the sheath flows F200 and the sample flow F100 are adjusted according to the size of the particulates to be analyzed or the like so that the particulates are made to flow in the state of being arrayed one after another.
In relation to the water flow system, there has also been developed a technology called micro flow cell or microfluidics in which two-dimensional or three-dimensional fine channels of about 1 mm or below in size formed from a plastic, glass or the like are used.
(ii) Optical System
In the optical system (ii), the particulates to be analyzed are irradiated with a laser beam, and fluorescence or scattered light generated from the particulates is detected (see (ii) in FIG. 18). Specifically, in the water flow system (i), the particulates are made to flow through a laser beam-irradiated part in the state of being arrayed one after another, and the fluorescence or scattered light generated from the particulate each time each of the individual particulates passes is detected by an optical detector on a parameter basis, so as to analyze the characteristics of each of the particulates.
(iii) Electric System
In the electric system (iii), the optical information detected in the optical system (ii) is converted into an electrical signal (voltage pulse) (see (iii) in FIG. 18). The electrical signal converted from the optical information is digitized, and a histogram is extracted based on the digitized data by use of an analyzing computer and software, so as to perform analysis.
(iv) Fractional Collection System
In the fractional collection system (iv), the particulates having undergone the measurement are separated and collected (see (iv) in FIG. 18). Representative fractional collection methods include a method in which a plus or minus electric charge is given to the particulates having undergone the measurement, and two deflection plates D with a potential difference therebetween are disposed on opposite sides of the flow cell so that the electrically charged particulates are each drawn toward either of the deflection plates according to the electric charge given thereto, whereby fractional collection of the particulates is achieved.
As above-mentioned, a technology for analysis and fractional collection of particulates in a channel (flow cell) is demanded in a wide range of fields, and the technology pertaining to the process of (i) to (iv) above has been being developed day by day. For example, JP-t-2004-500562 proposes a technology for stabilizing an astable flow (laminar flow) in which use is made of sheath flows with a thickening agent added thereto in order to provide the sheath flows with a viscosity higher than that of water.